This invention relates to an electro-pressure conversion control device in which a plate is driven by an electrical actuator to open and close the jetting hole, through which fluid flows, thereby to control the fluid pressure, and to such an electro-pressure conversion control device which is combined with a fuel injection valve device in which the needle valve is operated by a predetermined fuel pressure to inject fuel from the fuel injection hole.
There has been a strong demand for electrical control fluid because of the recent development of electronic technique, and it has been requested to improve the response characteristic of an electro-pressure conversion control device.
The electro-pressure conversion control device comprises, in combination, an electro-mechanical converter (hereinafter referred to as "an electrical actuator" when applicable) for converting an electrical signal into a mechanical drive force, and a pressure control valve for controlling the pressure of fluid.
It is true that the response characteristics of the electro-pressure conversion control device is determined by the response characteristic of the electrical actuator.
Heretofore, research has been conducted mainly to improve the response characteristic of the electrical actuator; however, it has been difficult to provide a suitable electrical actuator.
In general, the performance of an electrical actuator for fluid control is evaluated in (1) generated drive force, (2) drive displacement, and (3) response characteristic. Generally, the items (1) and (3) or (2) and (3) are contradictory to each other. If the response characteristic is increased, then the drive force and the displacement are decreased. Stated differently, if the drive force and the drive displacement are sacrificed to same extent, the actuator may have a high responsibility.
However, a conventional pressure control valve requires the drive force and the displacement which are relatively large, and therefore it is rather difficult to improve the response characteristic of the electrical actuator. Accordingly, it has been impossible for the prior art to provide an electro-pressure conversion control device high in response characteristic.
On the other hand, recently electrical control of a fuel injection device has been developed to improve the combustion efficiency of an automotive engine or the like thereby to economically use fuel, to purify exhaust gas, and to decrease noise.
A variety of electrical control methods for fuel injection valves have been proposed, and various fuel injection valves have been proposed, and some of them have been put in practical use.
One example of the conventional fuel injection have control methods is as shown in FIG. 1, which is extensively employed for a gasoline fuel injection. In the method, the needle valve 15 of a fuel injection valve A is driven directly by an electrical actuator 16 to control the fuel injection. The fuel injection device shown in FIG. 1 is advantageous in that it is simple in construction and can be readily controlled; however, it is disadvantageous in that, in order to provide a high injection pressure, it is necessary to drive the needle valve 15 with a large drive force, and accordingly in this case it is necessary to use an electrical actuator 16 large in capacity; that is it is necessary to use a heavy electrical actuator 16, with the result that the response characteristic is lowered. Therefore, the injection control method is not practical for the high pressure fuel injection in which the injection pressure is over 10 kg/cm.sup.2.
An electrical control system in which, as shown in FIG. 2, an electromagnetic valve is used to control an accumulator injection valve B has been proposed in the art. The system permits a high-pressure fuel injection. However, the system is disadvantageous in that, as it is necessary to provide an accumulator 17 or a pressure intensifying piston 18 and pipes therefor, the injection valve is rather intricate in construction, and the response characteristic is not sufficient in practical use.
Thus, it is difficult for the prior art to provide an electrical control type fuel injection device simple in construction, high in injection pressure and excellent in control characteristic.